In many laser uses and applications the laser beam energy must be transmitted through aberrating media such as the earth's atmosphere. The aberrations result in decreased energy delivery to a target. Two techniques for distortion compensation, known as "conventional" and "unconventional" have been developed and are available in the art. "Conventional" adaptive optics schemes use wavefront sensors combined with deformable mirrors. "Unconventional" adaptive optics schemes are primarily based on all-optical phase conjugation using nonlinear optics devices. Both techniques are reviewed in "Principles of Adaptive Optics", by R. K. Ryson, Ch. 3 (Academic Press, 1991).
In a conventional adaptive optics system as illustrated in FIG. 1, energy from a laser 10 is transmitted through suitable optics 12, a sampler 14, such as a beam splitter, a wavefront corrector means 16 and onto a target 18 through aberrating media. The wavefront that returns from the target is directed by sampler 14 to wavefront sensor (WFS) means 20 and is measured and, from this measurement, an optimum profile for the corrector deformable mirror is computed by control means 22. The outgoing laser beam is reflected off the corrector, and maximum energy delivered to the target.
In an unconventional adaptive optics system as illustrated in FIG. 2, a nonlinear optics phase conjugator 24 provides a nonlinear optics process such as four-wave-mixing or stimulated Brillouin scattering that is used to generate the conjugate of the electric field received through aberratory media from a beacon source 27. The beacon can be a target glint. With a perfect conjugation system, the conjugated beam retraces the path of the beacon (time-reversal), resulting in maximum energy delivered to the target. For long propagation paths and/or weak beacons, very large optical amplifications, on the order to 10.sup.10 -10.sup.15, are required in the combination of the conjugator 24 and the amplifier 26.